Network File System Version 4 C. Lever, Ed.
Internet-Draft Oracle
Intended status: Standards Track D. Noveck
Expires: July 13, 2018 NetApp
January 9, 2018
RPC-over-RDMA Version 2 Protocoldraft-cel-nfsv4-rpcrdma-version-two-06
Abstract
This document specifies an improved protocol for conveying Remote
Procedure Call (RPC) messages on physical transports capable of
Remote Direct Memory Access (RDMA), based on RPC-over-RDMA version 1.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on July 13, 2018.
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Internet-Draft RDMA Transport for RPC V2 January 20181. Introduction
Remote Direct Memory Access (RDMA) [RFC5040] [RFC5041] [IBARCH] is a
technique for moving data efficiently between end nodes. By
directing data into destination buffers as it is sent on a network
and placing it via direct memory access by hardware, the
complementary benefits of faster transfers and reduced host overhead
are obtained.
A protocol already exists that enables ONC RPC [RFC5531] messages to
be conveyed on RDMA transports. That protocol is RPC-over-RDMA
version 1, specified in [RFC8166]. RPC-over-RDMA version 1 is
deployed and in use, though there are some shortcomings to this
protocol, such as:
o The use of small Receive buffers force the use of RDMA Read and
Write transfers for small payloads, and limit the size of
backchannel messages.
o Lack of support for potential optimizations, such as remote
invalidation, that require changes to on-the-wire behavior.
To address these issues in a way that is compatible with existing
RPC-over-RDMA version 1 deployments, a new version of RPC-over-RDMA
is presented in this document. RPC-over-RDMA version 2 contains only
incremental changes over RPC-over-RDMA version 1 to facilitate
adoption of version 2 by existing version 1 implementations.
The major new feature in RPC-over-RDMA version 2 is extensibility of
the RPC-over-RDMA header. Extensibility enables narrow changes to
RPC-over-RDMA version 2 so that new optional capabilities can be
introduced without a protocol version change and while maintaining
interoperability with existing implementations.
New capabilities can be proposed and developed independently of each
other, and implementaters can choose among them, making it
straightforward to create and document experimental features and then
bring them through the standards process.
As part of this new extensibility feature set, a mechanism for
exchanging transport properties is introduced. This mechanism allows
RPC-over-RDMA version 2 connection endpoints to communicate
properties of their implementations, to request changes in properties
of the other endpoint, and to notify peer endpoints of changes to
properties that occur during operation.
In addition to extensibility, the default inline threshold value is
larger in RPC-over-RDMA version 2. This change is driven by the
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increase in average size of RPC messages containing common NFS
operations. With NFS version 4.1 [RFC5661] and later, compound
operations convey more data per RPC message. The default 1KB inline
threshold in RPC-over-RDMA version 1 prevents attaining the best
possible performance.
Support for Remote Invalidation has been introduced into RPC-over-
RDMA version 2. An RPC-over-RDMA responder can now request
invalidation of an STag as part of sending an RPC Reply, saving the
requester the effort of invalidating after message receipt. This new
feature is general enough to enable a requester to control precisely
when Remote Invalidation may be utilized by responders.
RPC-over-RDMA version 2 expands the repertoire of error codes to
enable extensibility, to report overruns of specific resources, and
to avoid requester retries when an error is permanent.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14 [RFC2119]
[RFC8174] when, and only when, they appear in all capitals, as shown
here.
3. Inline Threshold3.1. Terminology
The term "inline threshold" is defined in Section 4 of [RFC8166]. An
"inline threshold" value is the largest message size (in octets) that
can be conveyed in one direction on an RDMA connection using only
RDMA Send and Receive. Each connection has two inline threshold
values: one for messages flowing from requester-to-responder
(referred to as the "call inline threshold"), and one for messages
flowing from responder-to-requester (referred to as the "reply inline
threshold"). Inline threshold values are not advertised to peers via
the base RPC-over-RDMA version 2 protocol.
A connection's inline threshold determines when RDMA Read or Write
operations are required because the RPC message to be sent cannot be
conveyed via RDMA Send and Receive. When an RPC message does not
contain DDP-eligible data items, a requester prepares a Long Call or
Reply to convey the whole RPC message using RDMA Read or Write
operations.
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Internet-Draft RDMA Transport for RPC V2 January 20183.2. Motivation
RDMA Read and Write operations require that each data payload resides
in a region of memory that is registered with the RNIC. When an RPC
is complete, that region is invalidated, fencing it from the
responder.
Both registration and invalidation have a latency cost which is
insignificant compared to data handling costs. When a data payload
is small, however, the cost of registering and invalidating the
memory where the payload resides becomes a relatively significant
part of total RPC latency. Therefore the most efficient operation of
RPC-over-RDMA occurs when RDMA Read and Write operations are used for
large payloads, and avoided for small payloads.
When RPC-over-RDMA version 1 was conceived, the typical size of RPC
messages that did not involve a significant data payload was under
500 bytes. A 1024-byte inline threshold adequately minimized the
frequency of inefficient Long Calls and Replies.
Starting with NFS version 4.1 [RFC5661], NFS COMPOUND messages are
larger and more complex than before. With a 1024-byte inline
threshold, RDMA Read or Write operations are needed for frequent
operations that do not bear a data payload, such as GETATTR and
LOOKUP, reducing the efficiency of the transport.
To reduce the need to use Long Calls and Replies, RPC-over-RDMA
version 2 increases the default inline threshold size. This also
increases the maximum size of backward direction RPC messages.
3.3. Default Values
RPC-over-RDMA version 2 receiver implementations MUST support an
inline threshold of 4096 bytes, but MAY support larger inline
threshold values. A mechanism for discovering a peer's preferred
inline threshold value (not defined in this document) may be used to
optimize RDMA Send operations further. In the absense of such a
mechanism, senders MUST assume a receiver's inline threshold is 4096
bytes.
The new default inline threshold size is no larger than the size of a
hardware page on typical platforms. This conserves the resources
needed to Send and Receive base level RPC-over-RDMA version 2
messages, enabling RPC-over-RDMA version 2 to be used on a broad
variety of hardware.
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Internet-Draft RDMA Transport for RPC V2 January 20184. Remote Invalidation
An STag that is registered using the FRWR mechanism (in a privileged
execution context), or is registered via a Memory Window (in user
space), may be invalidated remotely [RFC5040]. These mechanisms are
available only when a requester's RNIC supports MEM_MGT_EXTENSIONS.
For the purposes of this discussion, there are two classes of STags.
Dynamically-registered STags are used in a single RPC, then
invalidated. Persistently-registered STags live longer than one RPC.
They may persist for the life of an RPC-over-RDMA connection, or
longer.
An RPC-over-RDMA requester may provide more than one STag in one
transport header. It may provide a combination of dynamically- and
persistently-registered STags in one RPC message, or any combination
of these in a series of RPCs on the same connection. Only
dynamically-registered STags using Memory Windows or FRWR (ie.
registered via MEM_MGT_EXTENSIONS) may be invalidated remotely.
There is no transport-level mechanism by which a responder can
determine how a requester-provided STag was registered, nor whether
it is eligible to be invalidated remotely. A requester that mixes
persistently- and dynamically-registered STags in one RPC, or mixes
them across RPCs on the same connection, must therefore indicate
which handles may be invalidated via a mechanism provided in the
Upper Layer Protocol. RPC-over-RDMA version 2 provides such a
mechanism.
The RDMA Send With Invalidate operation is used to invalidate an STag
on a remote system. It is available only when a responder's RNIC
supports MEM_MGT_EXTENSIONS, and must be utilized only when a
requester's RNIC supports MEM_MGT_EXTENSIONS (can receive and
recognize an IETH).
4.1. Backward-Direction Remote Invalidation
Existing RPC-over-RDMA protocol specifications [RFC8166] [RFC8167] do
not forbid direct data placement in the backward-direction, even
though there is currently no Upper Layer Protocol that may use it.
When chunks are present in a backward-direction RPC request, Remote
Invalidation allows the responder to trigger invalidation of a
requester's STags as part of sending a reply, the same as in the
forward direction.
However, in the backward direction, the server acts as the requester,
and the client is the responder. The server's RNIC, therefore, must
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support receiving an IETH, and the server must have registered the
STags with an appropriate registration mechanism.
5. Protocol Extensibility
The core RPC-over-RDMA version 2 header format is specified in
Section 7 as a complete and stand-alone piece of XDR. Any change to
this XDR description requires a protocol version number change.
5.1. Optional Features
RPC-over-RDMA version 2 introduces the ability to extend the core
protocol via optional features. Extensibility enables minor protocol
issues to be addressed and incremental enhancements to be made
without the need to change the protocol version. The key capability
is that both sides can detect whether a feature is supported by their
peer or not. With this ability, OPTIONAL features can be introduced
over time to an otherwise stable protocol.
The rdma_opttype field carries a 32-bit unsigned integer. The value
in this field denotes an optional operation that MAY be supported by
the receiver. The values of this field and their meaning are defined
in other Standards Track documents.
The rdma_optinfo field carries opaque data. The content of this
field is data meaningful to the optional operation denoted by the
value in rdma_opttype. The content of this field is not defined in
the base RPC-over-RDMA version 2 protocol, but is defined in other
Standards Track documents
When an implementation does not recognize or support the value
contained in the rdma_opttype field, it MUST send an RPC-over-RDMA
message with the rdma_xid field set to the same value as the
erroneous message, the rdma_proc field set to RDMA2_ERROR, and the
rdma_err field set to RDMA2_ERR_INVAL_OPTION.
5.2. Message Direction
Backward direction operation depends on the ability of the receiver
to distinguish between incoming forward and backward direction calls
and replies. This needs to be done because both the XID field and
the flow control value (RPC-over-RDMA credits) in the RPC-over-RDMA
header are interpreted in the context of each message's direction.
A receiver typically distinguishes message direction by examining the
mtype field in the RPC header of each incoming payload message.
However, RDMA2_OPTIONAL type messages may not carry an RPC message
payload.
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To enable RDMA2_OPTIONAL type messages that do not carry an RPC
message payload to be interpreted unambiguously, the rdma2_optional
structure contains a field that identifies the message direction. A
similar field has been added to the rpcrdma2_chunk_lists and
rpcrdma2_error structures to simplify parsing the RPC-over-RDMA
header at the receiver.
5.3. Documentation Requirements
RPC-over-RDMA version 2 may be extended by defining a new
rdma_opttype value, and then by providing an XDR description of the
rdma_optinfo content that corresponds with the new rdma_opttype
value. As a result, a new header type is effectively created.
A Standards Track document introduces each set of such protocol
elements. Together these elements are considered an OPTIONAL
feature. Each implementation is either aware of all the protocol
elements introduced by that feature, or is aware of none of them.
Documents describing extensions to RPC-over-RDMA version 2 should
contain:
o An explanation of the purpose and use of each new protocol element
added
o An XDR description of the protocol elements, and a script to
extract it
o A mechanism for reporting errors when the error is outside the
available choices already available in the base protocol or in
other extensions
o An indication of whether a Payload stream must be present, and a
description of its contents
o A description of interactions with existing extensions
The last bullet includes requirements that another OPTIONAL feature
needs to be present for new protocol elements to work, or that a
particular level of support be provided for some particular facility
for the new extension to work.
Implementers combine the XDR descriptions of the new features they
intend to use with the XDR description of the base protocol in this
document. This may be necessary to create a valid XDR input file
because extensions are free to use XDR types defined in the base
protocol, and later extensions may use types defined by earlier
extensions.
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The XDR description for the RPC-over-RDMA version 2 protocol combined
with that for any selected extensions should provide an adequate
human-readable description of the extended protocol.
6. Transport Properties6.1. Introduction to Transport Properties6.1.1. Property Model
A basic set of receiver and sender properties is specified in this
document. An extensible approach is used, allowing new properties to
be defined in future standards track documents.
Such properties are specified using:
o A code identifying the particular transport property being
specified.
o A nominally opaque array which contains within it the XDR encoding
of the specific property indicated by the associated code.
The following XDR types are used by operations that deal with
transport properties:
<CODE BEGINS>
typedef rpcrdma2_propid uint32;
struct rpcrdma2_propval {
rpcrdma2_propid rdma_which;
opaque rdma_data<>;
};
typedef rpcrdma2_propval rpcrdma2_propset<>;
typedef uint32 rpcrdma2_propsubset<>;
<CODE ENDS>
An rpcrdma2_propid specifies a particular transport property. In
order to allow easier XDR extension of the set of properties by
concatenating XDR files, specific properties are defined as const
values rather than as elements in an enum.
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An rpcrdma2_propval specifies a value of a particular transport
property with the particular property identified by rdma_which, while
the associated value of that property is contained within rdma_data.
A rdma_data field which is of zero length is interpreted as
indicating the default value or the property indicated by rdma_which.
While rdma_data is defined as opaque within the XDR, the contents are
interpreted (except when of length zero) using the XDR typedef
associated with the property specified by rdma_which. The receiver
of a message containing an rpcrdma2_propval MUST report an XDR error
[ cel: which error? BAD_XDR, or do we want to add a new one? ] if
the length of rdma_data is such that it extends beyond the bounds of
the message transferred.
In cases in which the rpcrdma2_propid specified by rdma_which is
understood by the receiver, the receiver also MUST report an XDR
error if either of the following occur: [ cel: which error? BAD_XDR,
or do we want to add a new one? ]
o The nominally opaque data within rdma_data is not valid when
interpreted using the property-associated typedef.
o The length of rdma_data is insufficient to contain the data
represented by the property-associated typedef.
Note that no error is to be reported if rdma_which is unknown to the
receiver. In that case, that rpcrdma2_propval is not processed and
processing continues using the next rpcrdma2_propval, if any.
A rpcrdma2_propset specifies a set of transport properties. No
particular ordering of the rpcrdma2_propval items within it is
imposed.
A rpcrdma2_propsubset identifies a subset of the properties in a
previously specified rpcrdma2_propset. Each bit in the mask denotes
a particular element in a previously specified rpcrdma2_propset. If
a particular rpcrdma2_propval is at position N in the array, then bit
number N mod 32 in word N div 32 specifies whether that particular
rpcrdma2_propval is included in the defined subset. Words beyond the
last one specified are treated as containing zero.
Propvalsubsets are useful in a number of contexts:
o In the specification of transport properties at connection, they
allow the sender to specify what subset of those are subject to
later change.
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o In responding to a request to modify a set of transport
properties, they allow the responding endpoint to specify the
subsets of those properties for which the requested change has
been performed or been rejected.
6.1.2. Transport Property Groups
Transport properties are divided into a number of groups
o A basic set of transport properties defined in this document. See
Section 6.2 for the complete list.
o Additional transport properties defined in future standards track
documents as specified in Section 6.4.1.
o Experimental transport properties being explored preparatory to
being considered for standards track definition. See the
description in Section 6.4.2.
6.1.3. Operations Related to Transport Properties
There are a number of operations defined in Section 6.3 which are
used to communicate and manage transport properties.
Prime among these is RDMA2_CONNPROP (defined in Section 6.3.1 which
serves as a means by which an endpoint's transport properties may be
presented to its peer, typically upon establishing a connection.
In addition, there are a set of related operations concerned with
requesting, effecting and reporting changes in transport properties:
o RDMA2_REQPROP (defined in Section 6.3.2 which serves as a way for
an endpoint to request that a peer change the values for a set of
transport properties.
o RDMA2_RESPROP (defined in Section 6.3.3 is used to report on the
disposition of each of the individual transport property changes
requested in a previous RDMA2_REQPROP.
o RDMA2_UPDPROP (defined in Section 6.3.4 is used to report an
unsolicited change in a transport property.
Unlike many other operation types, the above are not used to effect
transfer of RPC requests but are internal one-way information
transfers. However, a RDMA2_REQPROP and the corresponding
RDMA2_RESPROP do constitute an RPC-like remote call. The other
operations are not part of a remote call transaction.
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Internet-Draft RDMA Transport for RPC V2 January 20186.2. Basic Transport Properties
Although the set of transport properties is subject to later
extension, a basic set of transport properties is defined below in
Table 1.
In that table, the columns contain the following information:
o The column labeled "property" identifies the transport property
described by the current row.
o The column labeled "code" specifies the rpcrdma2_propid value used
to identify this property.
o The column labeled "XDR type" gives the XDR type of the data used
to communicate the value of this property. This data type
overlays the data portion of the nominally opaque field rdma_data
in a rpcrdma2_propval.
o The column labeled "default" gives the default value for the
property which is to be assumed by those who do not receive, or
are unable to interpret, information about the actual value of the
property.
o The column labeled "section" indicates the section (within this
document) that explains the semantics and use of this transport
property.
+---------+-----+------------------+----------------------+---------+
| propert | cod | XDR type | default | section |
| y | e | | | |
+---------+-----+------------------+----------------------+---------+
| Receive | 1 | uint32 | 4096 | 6.2.1 |
| Buffer | | | | |
| Size | | | | |
| Backwar | 2 | enum rpcrdma2_bk | RDMA2_BKREQSUP_INLIN | 6.2.2 |
| d | | reqsup | E | |
| Request | | | | |
| Support | | | | |
+---------+-----+------------------+----------------------+---------+
Table 1
Note that this table does not provide any indication regarding
whether a particular property can change or whether a change in the
value may be requested (see Section 6.3.2). Such matters are not
addressed by the protocol definition. An implementation may provide
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information about its readiness to make changed in a particular
property using the rdma_nochg field in the RDMA2_CONNPROP message.
A partner implementation can always request a change but peers MAY
reject a request to change a property for any reason.
Implementations are always free to reject such requests if they
cannot or do not wish to effect the requested change.
Either of the following will result in effective rejection requests
to change specific properties:
o If an endpoint does not wish to accept request to change
particular properties, it may reject such requests as described in
Section 6.3.3.
o If an endpoint does not support the RDMA2_REQPROP operation, the
effect would be the same as if every request to change a set of
property were rejected.
With regard to unrequested changes in transport properties, it is the
responsibility of the implementation making the change to do so in a
fashion that which does not interfere with the other partner's
continued correct operation (see Section 6.2.1).
6.2.1. Receive Buffer Size
The Receive Buffer Size specifies the minimum size, in octets, of
pre-posted receive buffers. It is the responsibility of the
participant sending this value to ensure that its pre-posted receives
are at least the size specified, allowing the participant receiving
this value to send messages that are of this size.
<CODE BEGINS>
const uint32 RDMA2_PROPID_RBSIZ = 1;
typedef uint32 rpcrdma2_prop_rbsiz;
<CODE ENDS>
The sender may use his knowledge of the receiver's buffer size to
determine when the message to be sent will fit in the preposted
receive buffers that the receiver has set up. In particular,
o Requesters may use the value to determine when it is necessary to
provide a Position-Zero read chunk when sending a request.
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o Requesters may use the value to determine when it is necessary to
provide a Reply chunk when sending a request, based on the maximum
possible size of the reply.
o Responders may use the value to determine when it is necessary,
given the actual size of the reply, to actually use a Reply chunk
provided by the requester.
Because there may be pre-posted receives with buffer sizes that
reflect earlier values of the buffer size property, changing this
property poses special difficulties:
o When the size is being raised, the partner should not be informed
of the change until all pending receives using the older value
have been eliminated.
o The size should not be reduced until the partner is aware of the
need to reduce the size of future sends to conform to this reduced
value. To ensure this, such a change should only occur in
response to an explicit request by the other endpoint (See
Section 6.3.2). The participant making the request should use
that lower size as the send size limit until the request is
rejected (See Section 6.3.3) or an update to a size larger than
the requested value becomes effective and the requested change is
no longer pending (See Section 6.3.4).
6.2.2. Backward Request Support
The value of this property is used to indicate a client
implementation's readiness to accept and process messages that are
part of backward-direction RPC requests.
<CODE BEGINS>
enum rpcrdma2_bkreqsup {
RDMA2_BKREQSUP_NONE = 0,
RDMA2_BKREQSUP_INLINE = 1,
RDMA2_BKREQSUP_GENL = 2
};
const uint32 RDMA2_PROPID_BRS = 2;
typedef rpcrdma2_bkreqsup rpcrdma2_prop_brs;
<CODE ENDS>
Multiple levels of support are distinguished:
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o The value RDMA2_BKREQSUP_NONE indicates that receipt of backward-
direction requests and replies is not supported.
o The value RDMA2_BKREQSUP_INLINE indicates that receipt of
backward-direction requests or replies is only supported using
inline messages and that use of explicit RDMA operations or other
form of Direct Data Placement for backward direction requests or
responses is not supported.
o The value RDMA2_BKREQSUP_GENL that receipt of backward-direction
requests or replies is supported in the same ways that forward-
direction requests or replies typically are.
When information about this property is not provided, the support
level of servers can be inferred from the backward- direction
requests that they issue, assuming that issuing a request implicitly
indicates support for receiving the corresponding reply. On this
basis, support for receiving inline replies can be assumed when
requests without read chunks, write chunks, or Reply chunks are
issued, while requests with any of these elements allow the client to
assume that general support for backward-direction replies is present
on the server.
6.3. New Operations
The proposed new operations are set forth in Table 2 below. In that
table, the columns contain the following information:
o The column labeled "operation" specifies the particular operation.
o The column labeled "code" specifies the value of opttype for this
operation.
o The column labeled "XDR type" gives the XDR type of the data
structure used to describe the information in this new message
type. This data overlays the data portion of the nominally opaque
field optinfo in an RDMA_OPTIONAL message.
o The column labeled "msg" indicates whether this operation is
followed (or not) by an RPC message payload.
o The column labeled "section" indicates the section (within this
document) that explains the semantics and use of this optional
operation.
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All relevant transport properties that the sender is aware of should
be included in rdma_start. Since support of this request is
OPTIONAL, and since each of the properties is OPTIONAL as well, the
sender cannot assume that the receiver will necessarily take note of
these properties and so the sender should be prepared for cases in
which the partner continues to assume that the default value for a
particular property is still in effect.
Values of the subset of transport properties specified by rdma_nochg
is not expected to change during the lifetime of the connection.
Generally, a participant will send a RDMA2_CONNPROP message as the
first message after a connection is established. Given that fact,
the sender should make sure that the message can be received by
partners who use the default Receive Buffer Size. The connection's
initial receive buffer size is typically 1KB, but it depends on the
initial connection state of the RPC-over-RDMA version in use.
Properties not included in rdma_start are to be treated by the peer
endpoint as having the default value and are not allowed to change
subsequently. The peer should not request changes in such
properties.
Those receiving an RDMA2_CONNPROP may encounter properties that they
do not support or are unaware of. In such cases, these properties
are simply ignored without any error response being generated.
6.3.2. RDMA2_REQPROP: Request Modification of Properties
The RDMA2_REQPROP message type allows an RPC-over-RDMA participant,
whether client or server, to request of its partner that relevant
transport properties be changed.
The rdma_xid field allows the request to be tied to a corresponding
response of type RDMA2_RESPROP (See Section 6.3.3.) In assigning the
value of this field, the sender does not need to avoid conflict with
xid's associated with RPC messages or with RDMA2_REQPROP messages
sent by the peer endpoint.
The partner need not change the properties as requested by the sender
but if it does support the message type, it will generate a
RDMA2_RESPROP message, indicating the disposition of the request.
The message definition for this operation is as follows:
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<CODE BEGINS>
struct rpcrdma2_reqprop {
rpcrdma2_propset rdma_want;
};
<CODE ENDS>
The rpcrdma2_propset rdma_want is a set of transport properties
together with the desired values requested by the sender.
6.3.3. RDMA2_RESPROP: Respond to Request to Modify Transport Properties
The RDMA2_RESPROP message type allows an RPC-over-RDMA participant to
respond to a request to change properties by its partner, indicating
how the request was dealt with.
The message definition for this operation is as follows:
<CODE BEGINS>
struct rpcrdma2_resprop {
rpcrdma2_propsubset rdma_done;
rpcrdma2_propsubset rdma_rejected;
rpcrdma2_propset rdma_other;
};
<CODE ENDS>
The rdma_xid field of this message must match that used in the
RDMA2_REQPROP message to which this message is responding.
The rdma_done field indicates which of the requested transport
property changes have been effected as requested. For each such
property, the receiver is entitled to conclude that the requested
change has been made and that future transmissions may be made based
on the new value.
The rdma_rejected field indicates which of the requested transport
property changes have been rejected by the sender. This may be
because of any of the following reasons:
o The particular property specified is not known or supported by the
receiver of the RDMA2_REQPROP message.
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o The implementation receiving the RDMA2_REQPROP message does not
support modification of this property.
o The implementation receiving the RDMA2_REQPROP message has chosen
to reject the modification for another reason.
The rdma_other field contains new values for properties where a
change is requested. The new value of the property is included and
may be a value different from the original value in effect when the
change was requested and from the requested value. This is useful
when the new value of some property is not as large as requested but
still different from the original value, indicating a partial
satisfaction of the peer's property change request.
The sender MUST NOT include rpcrdma2_propval items within rdma_other
that are for properties other than the ones for which the
corresponding property request has requested a change. If the
receiver finds such a situation, it MUST ignore the erroneous
rpcrdma2_propval items.
The subsets of properties specified by rdma_done, rdma_rejected, and
included in rdma_other MUST NOT overlap, and when ored together,
should cover the entire set of properties specified by rdma_want in
the corresponding request. If the receiver finds such an overlap or
mismatch, it SHOULD treat properties missing or within the overlap as
having been rejected.
6.3.4. RDMA2_UPDPROP: Update Transport Properties
The RDMA2_UPDPROP message type allows an RPC-over-RDMA participant to
notify the other participant that a change to the transport
properties has occurred. This is because the sender has decided,
independently, to modify one or more transport properties and is
notifying the receiver of these changes.
The message definition for this operation is as follows:
<CODE BEGINS>
struct rpcrdma2_updprop {
rpcrdma2_propset rdma_now;
};
<CODE ENDS>
rdma_now defines the new property values to be used.
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Internet-Draft RDMA Transport for RPC V2 January 20186.4. Extensibility6.4.1. Additional Properties
The set of transport properties is designed to be extensible. As a
result, once new properties are defined in standards track documents,
the operations defined in this document may reference these new
transport properties, as well as the ones described in this document.
A standards track document defining a new transport property should
include the following information paralleling that provided in this
document for the transport properties defined herein.
o The rpcrdma2_propid value used to identify this property.
o The XDR typedef specifying the form in which the property value is
communicated.
o A description of the transport property that is communicated by
the sender of RDMA2_CONNPROP and RDMA2_UPDPROP and requested by
the sender of RDMA2_REQPROP.
o An explanation of how this knowledge could be used by the
participant receiving this information.
o Information giving rules governing possible changes of values of
this property.
The definition of transport property structures is such as to make it
easy to assign unique values. There is no requirement that a
continuous set of values be used and implementations should not rely
on all such values being small integers. A unique value should be
selected when the defining document is first published as an internet
draft. When the document becomes a standards track document working
group should insure that:
o rpcrdma2_propid values specified in the document do not conflict
with those currently assigned or in use by other pending working
group documents defining transport properties.
o rpcrdma2_propid values specified in the document do not conflict
with the range reserved for experimental use, as defined in
Section 6.4.2.
Documents defining new properties fall into a number of categories.
o Those defining new properties and explaining (only) how they
affect use of existing message types.
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o Those defining new OPTIONAL message types and new properties
applicable to the operation of those new message types.
o Those defining new OPTIONAL message types and new properties
applicable both to new and existing message types.
When additional transport properties are proposed, the review of the
associated standards track document should deal with possible
security issues raised by those new transport properties.
6.4.2. Experimental Properties
Given the design of the transport properties data structure, it
possible to use the operations to implement experimental, possibly
unpublished, transport properties.
rpcrdma2_propid values in the range from 4,294,967,040 to
4,294,967,295 are reserved for experimental use and these values
should not be assigned to new properties in standards track
documents.
When values in this range are used there is no guarantee if
successful interoperation among independent implementations.
7. XDR Protocol Definition
This section contains a description of the core features of the RPC-
over-RDMA version 2 protocol, expressed in the XDR language
[RFC4506].
This description is provided in a way that makes it simple to extract
into ready-to-compile form. The reader can apply the following shell
script to this document to produce a machine-readable XDR description
of the RPC-over-RDMA version 1 protocol without any OPTIONAL
extensions.
<CODE BEGINS>
#!/bin/sh
grep '^ *///' | sed 's?^ /// ??' | sed 's?^ *///$??'
<CODE ENDS>
That is, if the above script is stored in a file called "extract.sh"
and this document is in a file called "spec.txt" then the reader can
do the following to extract an XDR description file:
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<CODE BEGINS>
sh extract.sh < spec.txt > rpcrdma_corev2.x
<CODE ENDS>
Optional extensions to RPC-over-RDMA version 2, published as
Standards Track documents, will have similar means of providing XDR
that describes those extensions. Once XDR for all desired extensions
is also extracted, it can be appended to the XDR description file
extracted from this document to produce a consolidated XDR
description file reflecting all extensions selected for an RPC-over-
RDMA implementation.
7.1. Code Component License
Code components extracted from this document must include the
following license text. When the extracted XDR code is combined with
other complementary XDR code which itself has an identical license,
only a single copy of the license text need be preserved.
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<CODE BEGINS>
/// /*
/// * Copyright (c) 2010-2017 IETF Trust and the persons
/// * identified as authors of the code. All rights reserved.
/// *
/// * The authors of the code are:
/// * B. Callaghan, T. Talpey, C. Lever, and D. Noveck.
/// *
/// * Redistribution and use in source and binary forms, with
/// * or without modification, are permitted provided that the
/// * following conditions are met:
/// *
/// * - Redistributions of source code must retain the above
/// * copyright notice, this list of conditions and the
/// * following disclaimer.
/// *
/// * - Redistributions in binary form must reproduce the above
/// * copyright notice, this list of conditions and the
/// * following disclaimer in the documentation and/or other
/// * materials provided with the distribution.
/// *
/// * - Neither the name of Internet Society, IETF or IETF
/// * Trust, nor the names of specific contributors, may be
/// * used to endorse or promote products derived from this
/// * software without specific prior written permission.
/// *
/// * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS
/// * AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED
/// * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
/// * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
/// * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
/// * EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
/// * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
/// * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
/// * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
/// * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
/// * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
/// * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
/// * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
/// * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
/// * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
/// */
<CODE ENDS>
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Internet-Draft RDMA Transport for RPC V2 January 20187.2.1. Presence Of Payload
o When the rdma_proc field has the value RDMA2_MSG, an RPC Payload
Stream MUST follow the Transport Header Stream in the Send buffer.
o When the rdma_proc field has the value RDMA2_ERROR, an RPC Payload
Stream MUST NOT follow the Transport Header Stream.
o When the rdma_proc field has the value RDMA2_OPTIONAL, all, part
of, or no RPC Payload Stream MAY follow the Transport header
Stream in the Send buffer.
7.2.2. Message Direction
Implementations of RPC-over-RDMA version 2 are REQUIRED to support
backwards direction operation as described in [RFC8167]. RPC-over-
RDMA version 2 introduces the rdma_direction field in its transport
header to optimize the process of distinguishing between forward- and
backwards-direction messages.
The rdma_direction field qualifies the value contained in the
transport header's rdma_xid field. This enables a receiver to
reliably avoid performing an XID lookup on incoming backwards-
direction Call messages.
In general, when a message carries an XID that was generated by the
message's receiver (that is, the receiver is acting as a requester),
the message's sender sets the rdma_direction field to REPLY (1).
Otherwise the rdma_direction field is set to CALL (0). For example:
o When the rdma_proc field has the value RDMA2_MSG or RDMA2_NOMSG,
the value of the rdma_direction field MUST be the same as the
value of the associated RPC message's msg_type field.
o When the rdma_proc field has the value RDMA2_OPTIONAL and a whole
or partial RPC message payload is present, the value of the
rdma_optdir field MUST be the same as the value of the associated
RPC message's msg_type field.
o When the rdma_proc field has the value RDMA2_OPTIONAL and no RPC
message payload is present, a Requester MUST set the value of the
rdma_optdir field to CALL, and a Responder MUST set the value of
the rdma_optdir field to REPLY. The Requester chooses a value for
the rdma_xid field from the XID space that matches the message's
direction. Requesters and Responders set the rdma_credit field in
a similar fashion: a value is set that is appropriate for the
direction of the message.
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o When the rdma_proc field has the value RDMA2_ERROR, the direction
of the message is always Responder-to-Requester (REPLY).
7.2.3. Remote Invalidation
To request Remote Invalidation, a requester MUST set the value of the
rdma_inv_handle field in an RPC Call's transport header to a non-zero
value that matches one of the rdma_handle fields in that header. If
none of the rdma_handle values in the Call may be invalidated by the
responder, the requester MUST set the RPC Call's rdma_inv_handle
field to the value zero.
If the responder chooses not to use Remote Invalidation for this
particular RPC Reply, or the RPC Call's rdma_inv_handle field
contains the value zero, the responder MUST use RDMA Send to transmit
the matching RPC reply.
If a requester has provided a non-zero value in the RPC Call's
rdma_inv_handle field and the responder chooses to use Remote
Invalidation for the matching RPC Reply, the responder MUST use RDMA
Send With Invalidate to transmit that RPC reply, and MUST use the
value in the RPC Call's rdma_inv_handle field to construct the Send
With Invalidate Work Request.
7.2.4. Transport Errors
Error handling works the same way in RPC-over-RDMA version 2 as it
does in RPC-over-RDMA version 1, with the addition of several new
error codes, and error messages never flow from requester to
responder. version 1 error handling is described in Section 5 of
[RFC8166].
In all cases below, the responder copies the values of the rdma_xid
and rdma_vers fields from the incoming transport header that
generated the error to transport header of the error response. The
responder sets the rdma_proc field to RDMA2_ERROR, and the
rdma_credit field is set to the credit grant value for this
connection.
RDMA2_ERR_VERS
This is the equivalent of ERR_VERS in RPC-over-RDMA version 1.
The error code value, semantics, and utilization are the same.
RDMA2_ERR_INVAL_PROC
If a responder recognizes the value in the rdma_vers field, but it
does not recognize the value in the rdma_proc field, it MUST set
the rdma_err field to RDMA2_ERR_INVAL_PROC.
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RDMA2_ERR_BAD_XDR
If a responder recognizes the values in the rdma_vers and
rdma_proc fields, but the incoming RPC-over-RDMA transport header
cannot be parsed, it MUST set the rdma_err field to
RDMA2_ERR_BAD_XDR. The error code value of RDMA2_ERR_BAD_XDR is
the same as the error code value of ERR_CHUNK in RPC-over-RDMA
version 1. The responder MUST NOT process the request in any way
except to send an error message.
RDMA2_ERR_READ_CHUNKS
If a requester presents more DDP-eligible arguments than the
responder is prepared to Read, the responder MUST set the rdma_err
field to RDMA2_ERR_READ_CHUNKS, and set the rdma_max_chunks field
to the maximum number of Read chunks the responder can receive and
process.
If the responder implementation cannot handle any Read chunks for
a request, it MUST set the rdma_max_chunks to zero in this
response. The requester SHOULD resend the request using a
Position-Zero Read chunk. If this was a request using a Position-
Zero Read chunk, the requester MUST terminate the transaction with
an error.
RDMA2_ERR_WRITE_CHUNKS
If a requester has constructed an RPC Call message with more DDP-
eligible results than the server is prepared to Write, the
responder MUST set the rdma_err field to RDMA2_ERR_WRITE_CHUNKS,
and set the rdma_max_chunks field to the maximum number of Write
chunks the responder can process and return.
If the responder implementation cannot handle any Write chunks for
a request, it MUST return a response of RDMA2_ERR_REPLY_RESOURCE
(below). The requester SHOULD resend the request with no Write
chunks and a Reply chunk of appropriate size.
RDMA2_ERR_SEGMENTS
If a requester has constructed an RPC Call message with a chunk
that contains more segments than the responder supports, the
responder MUST set the rdma_err field to RDMA2_ERR_SEGMENTS, and
set the rdma_max_segments field to the maximum number of segments
the responder can process.
RDMA2_ERR_WRITE_RESOURCE
If a requester has provided a Write chunk that is not large enough
to convey a DDP-eligible result, the responder MUST set the
rdma_err field to RDMA2_ERR_WRITE_RESOURCE.
The responder MUST set the rdma_chunk_index field to point to the
first Write chunk in the transport header that is too short, or to
zero to indicate that it was not possible to determine which chunk
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is too small. Indexing starts at one (1), which represents the
first Write chunk. The responder MUST set the rdma_length_needed
to the number of bytes needed in that chunk in order to convey the
result data item.
Upon receipt of this error code, a responder MAY choose to
terminate the operation (for instance, if the responder set the
index and length fields to zero), or it MAY send the request again
using the same XID and more reply resources.
RDMA2_ERR_REPLY_RESOURCE
If an RPC Reply's Payload stream does not fit inline and the
requester has not provided a large enough Reply chunk to convey
the stream, the responder MUST set the rdma_err field to
RDMA2_ERR_REPLY_RESOURCE. The responder MUST set the
rdma_length_needed to the number of Reply chunk bytes needed to
convey the reply.
Upon receipt of this error code, a responder MAY choose to
terminate the operation (for instance, if the responder set the
index and length fields to zero), or it MAY send the request again
using the same XID and larger reply resources.
RDMA2_ERR_INVAL_OPTION
A responder MUST set the rdma_err field to RDMA2_ERR_INVAL_OPTION
when an RDMA2_OPTIONAL message is received and the responder does
not recognize the value in the rdma_opttype field.
RDMA2_ERR_SYSTEM
If some problem occurs on a responder that does not fit into the
above categories, the responder MAY report it to the sender by
setting the rdma_err field to RDMA2_ERR_SYSTEM.
This is a permanent error: a requester that receives this error
MUST terminate the RPC transaction associated with the XID value
in the rdma_xid field.
8. Protocol Version Negotiation
When an RPC-over-RDMA version 2 client establishes a connection to a
server, the first order of business is to determine the server's
highest supported protocol version.
As with RPC-over-RDMA version 1, a client MUST assume the ability to
exchange only a single RPC-over-RDMA message at a time until it
receives a valid non-error RPC-over-RDMA message from the server that
reports the server's credit limit.
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First, the client sends a single valid RPC-over-RDMA message with the
value two (2) in the rdma_vers field. Because the server might
support only RPC-over-RDMA version 1, this initial message can be no
larger than the version 1 default inline threshold of 1024 bytes.
8.1. Server Does Support RPC-over-RDMA Version 2
If the server does support RPC-over-RDMA version 2, it sends RPC-
over-RDMA messages back to the client with the value two (2) in the
rdma_vers field. Both peers may use the default inline threshold
value for RPC-over-RDMA version 2 connections (4096 bytes).
8.2. Server Does Not Support RPC-over-RDMA Version 2
If the server does not support RPC-over-RDMA version 2, it MUST send
an RPC-over-RDMA message to the client with the same XID, with
RDMA2_ERROR in the rdma_proc field, and with the error code
RDMA2_ERR_VERS. This message also reports a range of protocol
versions that the server supports. To continue operation, the client
selects a protocol version in the range of server-supported versions
for subsequent messages on this connection.
If the connection is lost immediately after an RDMA2_ERROR /
RDMA2_ERR_VERS message is received, a client can avoid a possible
version negotiation loop when re-establishing another connection by
assuming that particular server does not support RPC-over-RDMA
version 2. A client can assume the same situation (no server support
for RPC-over-RDMA version 2) if the initial negotiation message is
lost or dropped. Once the negotiation exchange is complete, both
peers may use the default inline threshold value for the transport
protocol version that has been selected.
8.3. Client Does Not Support RPC-over-RDMA Version 2
If the server supports the RPC-over-RDMA protocol version used in
Call messages from a client, it MUST send Replies with the same RPC-
over-RDMA protocol version that the client uses to send its Calls.
8.4. Security Considerations
The security considerations for RPC-over-RDMA version 2 are the same
as those for RPC-over-RDMA version 1.
8.4.1. Security Considerations (Transport Properties)
Like other fields that appear in each RPC-over-RDMA header, property
information is sent in the clear on the fabric with no integrity
protection, making it vulnerable to man-in-the-middle attacks.
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